most businesses have -- and again, it's technology smaller than a hockey puck. people see them if they are aware of them. the little dome can often contain three or four camera heads, sometimes l.e.d. lighting at night. >> this is a radical change from five years ago. all of our cities are wired. some are the official cameras for the boston police department. but almost every business and every person. that's why officials came out early on and said preserve it it. otherwise, those businesses might ordinarily lose that after a couple days. so it needs to be preserved, get to the government. it it takes i'm to get through all that. once you know about the location, and once you know the timeframe, officials can get through that rel relatively rapidly. >> quite extraordinary yesterday. people taking the air shuttle and flying from boston logan to let's say new york were stopped. heard an announcement. before you leave here, ask yourself, do you have any evidence? did you take any pictures of the marathon? i arrived at the amtrak station yesterday and heard the ann